The present invention relates to a method for executing wire bonding and more particularly to a wire bonding method that involves a countermeasure against bonding failure at a bond point where bonding is made.
In general, for wire bonding methods for bonding a ball formed at a tip end of a bonding wire (merely called “wire”) to a first bond point and then connecting the first bond point to a second bond point with the wire, two methods shown in FIG. 4 and FIG. 5 are used. Also as a typical case, an exemplary wire bonding method can be found in, U.S. Pat. No. 5,111,989, the disclosure which is hereby incorporated by reference. In FIGS. 4 and 5, on a circuit board 1 comprising a ceramic board or print board or lead frame or the like, a die 3 whereon a pad 2 is formed is mounted; and an interconnect wiring 4 is formed on the circuit board 1.
In the first wire bonding method, as shown in FIG. 4, the pad 2 is the first bond point and the interconnect wiring 4 is the second bond point. Since the pad 2 is the first bond point, a ball 11 formed at the tip end of a wire 10 is bonded directly to the pad 2 that is the first bond point.
In the second wire bonding method, as shown in FIG. 5, conversely to that described above, the interconnect wiring 4 is the first bond point, and the pad 2 is the second bond point. In this method, since the pad 2 is the second bond point, a bump 22 is formed beforehand on the pad 2.
The first wire bonding method is first described with reference to FIG. 4.
In step (a), a ball 11 is formed by an electric torch (not shown in the drawings) at the tip end of the wire 10 that passes through a clamper 5 and further passes through a capillary 6, and then the clamper 5 is opened.
Next, in step (b), the capillary 6 descends and bonds the ball 11 to the pad 2 that is the first bond point, thus forming the first bonding part 12.
Next, in step (c), the capillary 6 ascends as far as a reverse starting point A, paying out the wire 10.
Then, in (d), a reverse movement is effected, causing the capillary 6 to move horizontally as far as a bend formation point B in a direction opposite from the interconnect wiring 4 that is the second bond point. As a result, the wire 10 takes on a shape such that it inclines from the first bonding part 12 to the bend formation point B, and a bent part 13 of the wire is formed at the portion of the bend formation point B.
In next step (e), the capillary 6 ascends as far as a loop top point C as it pays out the wire 10.
After the step (e), the capillary 6 is moved in step (f) to directly above the interconnect wiring 4 that is the second bond point, and then it descends and bonds the wire 10 to the interconnect wiring 4 to make a second bonding part 14.
Next, the clamper 5 and capillary 6 ascend together in step (g), the clamper 5 closes during this ascending movement, and the wire 10 is cut at the base of the second bonding part 14.
FIG. 5 shows the second wire bonding method
In this method, in step (a), a ball 20 is formed by an electric torch (not shown) at the tip end of the wire 10, and then the clamper 5 is opened.
In the next step (b), the capillary 6 descends and bonds the ball 20 to the pad 2 that is the second bond point, thus forming a bump 22.
After this step (b), the clamper 5 and capillary 6 ascend in step (c) together with the clamper 5 closed during this ascending movement, and the wire 10 is cut at the base of the bump 22, thus forming the bump 22 on the pad 2, with the tail 23 of the wire 10 left extended out of the capillary 6.
Next, a ball 24 is formed by an electric torch (not shown) in the tail 23 in step (d); and then the clamper 5 is opened, and it is moved above the interconnect wiring 4 that is the first bond point.
In the next step (e), the capillary 6 descends and bonds the ball 24 to the interconnect wiring 4 that is the first bond point, thus forming a first bonding part 25.
The capillary 6 then ascends in step (f) as far as the reverse starting point A, paying out the wire 10.
In step (g), a reverse movement is then effected causing the capillary 6 to move horizontally as far as the bend formation point B in a direction opposite from the pad 2 that is the second bond point. As a result, the wire 10 takes on a shape such that it inclines from the first bonding part 25 to the bend formation point B, and a bent part 26 of the wire is formed at the portion of the bend formation point B.
Next, in step (h), the capillary 6 ascends as far as the loop top point C, paying out the wire 10.
After the step (h), the capillary 6 is moved in step (i) to directly above the pad 2 that is the second bond point; and then the capillary 6 descends and bonds the wire 10 to the pad 2, making the pad a second bonding part 27.
Next, in step (j), the clamper 5 and capillary 6 ascend together, the clamper 5 closes during this ascending movement, cutting the wire 10 at the base of the second bonding part 27.
In the above-described methods, in cases where the joining strength for the first bonding part 12 in the method of FIG. 4 or for the first bonding part 25 in the method of FIG. 5 is insufficient, the first bonding part 12 or 25 may peel away from the pad 2 or the interconnect wiring 4 when the capillary 6 ascends step (c) of FIG. 4 or in step (f) of FIG. 5. Methods for detecting such bonding failure at the first bonding part are disclosed in, for instance, U.S. Pat. No. 5,058,797, Japanese Patent Application Laid-Open (Kokai) Nos. H7-94545 (Japanese Patent No. 3,041,812) and 2003-347369. Please note that exemplary method for detecting bonding failure can be found in U.S. Pat. No. 5,058,797, the disclosure of which is hereby incorporated.
Furthermore, in cases where the joining strength for the bump 22 is insufficient, when the wire 10 is cut during in steps (b) and (c), the bump 22 would peel away from the pad 2 and is raised together with the capillary 6. At least one, U.S. Pat. No. 5,058,797, Japanese Patent Application Laid-Open (Kokai) Nos. 11-191564 and 2000-306940, for instance, disclose methods for detecting such bonding failures at the bump part.
In the related art described above, when a first bonding part non-bonding (bonding failure) or bump part non-bonding (bonding failure) occurs, an abnormality signal is output, and the bonding apparatus is stopped. Since the apparatus will be in a stopped state until a worker arrives to fix the problems, productivity is poor, which is a problem.